(1) Field of the Invention:
This invention relates to a slider for a passive seat belt system in which a webbing for protecting an occupant of an automotive vehicle is automatically applied to him after he sits in a seat of the automotive vehicle. This invention is also concerned with a passive seat belt system making use of such a slider.
(2) Description of the Related Art:
A passive seat belt system is constructed, for example, of a rail provided on a interior roofside of a vehicle substantially along a longitudinal axis of the vehicle, a slider provided inside the rail displaceably back and forth substantially along the longitudinal axis of the vehicle, and a webbing fastened to the slider. The slider is caused to move by a drive member arranged inside the rail, such as a tape or wire, so that when an occupant gets off the vehicle, the slider is caused to move toward the front of the vehicle to have the webbing separated from an associated seat but when the occupant has sat in a seat, the slider is caused to move toward the rear of the vehicle to have the webbing approached toward the seat and hence applied to the occupant. The above-described movements of the slider are controlled by detecting opening and closure of an associated door.
A slider suitable for use in such a passive seat belt system has a webbing-fastening head portion at one end thereof and a slider leg portion at the other end thereof. The slider receives a drive force from a drive member via a cover layer formed on the outer periphery of the slider leg portion and made of a synthetic resin.
Such a slider is required to withstand a large tensile force which is applied to an occupantrestraining webbing in the event of an emergency of the vehicle. In order to meet this requirement, it is made of a high-strength material such as high carbon steel and moreover, includes a thicker portion so as to enhance its strength at a part exposed to the tensile strength. For the fabrication of a slider of the above structure, a fabrication process has been adopted that a slider main body is formed by hot forging, casting or press forming and a synthetic resin is then applied on the outer circumference of a slider leg portion at which the slider main body is received slidably in an associated rail.
When a slider main body is fabricated by hot forging as in the conventional process mentioned above by way of example, problems arise due to the high strength of its material that facilities having high working ability are required, many steps are needed to form a slider from the material and the slider tends to have poor precision.
When a slider main body is fabricated by casting on the other hand, the slider main body tends to contain one or more cavities to have poor strength and also requires post working, thereby failing to reduce the fabrication cost.
In addition, the fabrication of a slider main body by press forming requires, as post working, to weld plural parts together or to secure them together with rivets so as to form a thicker portion of a slider leg portion. Accordingly, more fabrication steps are required and more complex parts control and management are needed.
With a view toward solving such problems, it has been proposed, as in the invention disclosed in Japanese Utility Model Laid-Open No. 134459/1986, to form a slider blank from plate material of a uniform thickness by stamping and then to forge the slider blank to form a thicker portion which serves as a slider leg portion.
Since the slider blank is formed by stamping and the thicker portion serving as a slider leg portion is thereafter formed, the slider according to the invention of the above patent publication is however accompanied by problems such that forging is required for each slider blank, the precision of the main portion of the slider is reduced due to high impacts applied upon forging, more steps are required in total upon mass fabrication of sliders and the fabrication cost increases. Where the leg portion of the slider is covered with a synthetic layer, it is preferable as a countermeasure for the prevention of cracking at the time of molding that the thickness of the cover be uniform. It is however not very easy to form, by forging, a slider leg portion having a shape analogous to the shape of the final product.